Some embodiments described herein relate generally to methods and apparatus for the detection and correction of distortion of the transmitted signal in an optical transmitter. In particular, but not by way of limitation, some of the embodiments described herein relate to methods and apparatus for the detection and correction of frequency-based distortion of the transmitted signal associated with both an analog implementation and a digital implementation of an optical transmitter.
High data rate optical networks (e.g., 100 Gbit/s and beyond) can be enabled by, for example, an optical M-ary quadrature amplitude modulation (M-QAM) scheme with digital signal processing (DSP). Transmitter side serializer/deserializer (SerDes) and digital-to-analog converters (DACs) are building blocks for spectrally-efficient, multi-level signal generation and spectral manipulation. High data rate communication interfaces, however, can impose high signal integrity demands that are difficult to accomplish without the use of pre-emphasis and/or post-compensation techniques. Known methods of pre-emphasis based signal correction include providing variable analog peaking in a SerDes along the transmitter-side orientation (TX) or the use of a digital filter in conjunction with a DAC.
Adjusting the pre-emphasis parameters of the SerDes TX can be particularly difficult if the interconnect properties are not known at the time of manufacture and the pre-emphasis parameters cannot be set accurately in the factory. This is typically the case when pluggable photonic elements are used, where the properties of the photonic elements can vary dramatically from vendor to vendor and over generations of photonic elements. Hence, this presents challenges for component designers and board designers that can prevent in-factory calibration and the correction of distortion.
Accordingly, a need exists for methods and apparatus for automatically setting the SerDes TX pre-emphasis parameters for a specific optical transmitter system. Such optimization can be implemented at the time of port turn up, after reset, or continuously optimized in the background to compensate for signal power fluctuations due to, for example, temperature effects and/or temporal effects.